The principal objective of this project is to study the mechanisms by which simple neural networks process information with particular emphasis on mechanisms of learning. The nervous system of Hermissenda crassicornis has proven to be an excellent model for information processing at several levels: sensory transduction by photoreceptors and hair cells, analysis of synaptic circuitry, changes in synaptic circuitry produced by conditioning paradigms administered to intact animals as well as to isolated nervous systems, membrane properties modified by conditioning, identification of critical developmental stages for the neural networks studied as well as stages critical for learning. Techniques employed thus far to pursue these questions include: simultaneous intracellular recording from multiple neural elements, paired stimulation of the visual and vestibular pathways using a rotating table, iontophonesis of fluorescent dyes and electron dense materials, automated behavioral monitoring of intact Hermissenda. Other methods include biochemical and developmental approaches to the above problems. These include mariculture, subcellular fractionation protein phosphorylation analysis, and uptake of neurotransmitter precursors.